Jon Snow attacked the social media giant's "lack of activity" in the keynote MacTaggart lecture at the Edinburgh TV Festival.

U.K. TV news legend Jon Snow on Wednesday challenged Facebook over its role in the rise of fake news.

In the annual MacTaggart speech at the Edinburgh Television Festival, the ITN journalist and longest-running host of Channel 4 News, which he has presented since 1989, said the social media giant's lack of strong action could become a threat to democracy.

"Many news organizations including my own, have asked too few questions about the apparent miracle of Facebook’s reach," Snow said in his speech, entitled "The Worst and Best of Times."

"For us at Channel 4 News, it has been invaluable in helping us to deliver our remit — to reach young viewers, to innovate and to get attention for some of the world’s most important stories. But the other side of the issue — the dark, cancerous side — Facebook enabled the story 'Pope endorses Trump for President' to engage more than a million people during the U.S. elections."

Added the anchor: "That same algorithm that prioritized many amazing reports of ours, also prioritized fakery on a massive scale."

Snow concluded: "Facebook has a moral duty to prioritize veracity over virality. It is fundamental to our democracy. Facebook’s lack of activity in this regard could prove a vast threat to democracy."

The British TV journalist also argued that "Facebook’s principles are seldom explained in detail and can change overnight at Mr. Zuckerberg’s whim," calling on the social media giant and Google to play a role on helping to finance serious and reliable news.

"While the reach of Facebook video exceeds that of conventional broadcasting, the revenue provided doesn’t even come close," he said. "And Facebook themselves have provided publishers with the most nominal of sums and certainly not the rate for the job. Rather than simply trying to take down the fakery, there has to be an incentive for Facebook to pay the rate for high-quality news and encourage the development of a global bedrock of truths rooted in their offer to the quarter of the world’s online audience."

He criticized the Facebook boss more than once during his speech.

"Indeed, when you read Zuckerberg's manifesto for the future, he seems to think Facebook will invent and establish quality journalism," Snow said. "There is no need to, Mr. Zuckerberg. It already exists, independent of Facebook. In fact, the duopoly of Facebook and Google has decimated the market in digital revenue that many hoped would sustain quality journalism for years to come. Now we all need to work together and find another way of supporting it — before it’s too late."

The shortcomings of digital media also featured in other sections of Snow's Wednesday lecture. "The explosion of digital media has filled neither the void left by the decimation of the local newspaper industry – nor connected us any more effectively with the left behind, the disadvantaged, the excluded," he argued. "Never have we been more accessible to the public nor in some ways more disconnected from the lives of others."

Snow also expressed his concern about possible changes to British law that could put journalists in danger.

"There are dark clouds threatening us: The Law Commission is working on a new espionage bill. It follows on from the Snoopers Charter, which enables the police to access private communications without judicial oversight. It’s now proposed effectively to criminalize journalists and their sources, treating us like spies," he said. "It suggests anyone publishing or broadcasting leaked government information could land in jail for up to 14 years."

Snow concluded his speech by saying: "In the age where everyone is a publisher, public service broadcast journalism has never been more vital," and that "humanity needs to match the dramatic growth of social media with a rebirth of social mobility."

Snow called on the TV industry people in attendance, saying: "If we in this room can bind together, with our colleagues and, yes, even rivals across the world, we can prevail in the pursuit of truth. I shall go on doing what I do, as long as they let me. And I know that very many of you will do so, too. It’s the worst and best of times to be on deck, … but it still has all the potential to prove to be the Golden Age. Let's seize it!"

The MacTaggart lecture traditionally opens the festival and sets the tone for debate during the event on issues confronting the industry. Previous speakers have included Kevin Spacey, Vice CEO Shane Smith, who gave the lecture last year, three Murdochs (Rupert, James and Elisabeth), Alphabet executive chairman Eric Schmidt, Ted Turner and Veep creator Armando Iannucci.